Disposable impressing sheets



DEQ. 29, 1970 1 F HECHTMAN ETAL 3,551,177

DISPOSABLE IMPRES S ING SHEET S Filed sept. ze, 1967 United States Patent O 3,551,177 DISPOSABLE IMPRESSING SHEETS .lohn F. Hechtman and Harold R. Ames, Munising, Mich.,

assignors to KimberlyhClark Corporation, Neenah, Wis., a corporation of Delaware Continuation-impart of application Ser. No. 648,072,

June 22, 1967. This application Sept. 26, 1967,

Ser. No. 670,671

Int. Cl. B31f 1/00 U.S. Cl. 117-11 17 Claims ABSTRACT F THE DISCLOSURE A low cost patterned impression sheet for embossing decorative patterns into the surface of fiberboard panels, Adecorative laminates, or the like. The sheet comprises -a flexible web having a release coating on one surface and a predetermined threedimensional pattern of substantially incompressible and non-crushable material applied to the other surface. The patterned coating is of sufficient thickness to emboss the surface of the fiberboard when the sheet is interposed between a fiberboard substrate and a caul plate or press platen during conventional pressing operations. The patterned coating may be applied by first embossing the paper sheet and backfilling the embossed areas, or by printing a raised pattern on the sheet. A method for making the impression sheet is also described.

BACKGROUND OF THE INVENTION This is a continuation-impart of copending application Ser. No. 648,072, filed June 22, 1967, now abandoned.

This invention relates to disposable sheets having a three-dimensional pattern of substantially incompressible and non-crushable material applied to one surface for use as single or multiple-use master impressing sheets in embossing decorative patterns on iiberboard panels or the like.

In the manufacture of pressed fiberboard and hardboard panels it has recently become desirable to impart a textured surface thereto in the for-rn of a decorative embossing. Boards of this type are now manufactured with surface finishes which simulate expensive wood grains, leather, cloth, ceramic tile patterns, geometric designs, and other decorative patterns.

One process for the manufacture of iiberboard is to wet-form coarse cellulose fibers into a low density mat and subsequently hot press the moist fibrous mat between steel caul plates or press platens to consolidate and cure the mat. In another process, the fiber mat is completely dried before the pressing operation.

The binder for the fibers may be the natural lgnin which remains afterl the pulping process, a curable or thermosetting resin, or any similar resin which may be added before or during mat formation.

In one method of providing an improved surface on iiberboard, a finished sheet of paper, either plain or printed, is applied to one surface of a thick mat of coarse fibers and the paper sheet and mat are consolidated into a unitary board under heat and pressure. The paper provides v greatly improved surface qualities, due to the finer fibers used, and the hot pressing provides an integral bonding between the paper and the underlying coarser fibers. In other constructions, and especially when a dry pressing process is used, the top paper layer is generally omitted and the pressed board is finished by applying an opaque coating of paint, plastic enamel or the like.

When three-dimensional effects are desired in the fiberboard surface to improve the decorative effect, the top caul plate is provided with an engraved or etched embossing pattern. For example, if thepaperA sheet has va ice simulated Wood grain pattern printed on its surface, the top caul plate may be engraved with a similar grain pattern. The result, after pressing is a hardboard product which has both the appearance and surface texture of real wood.

Etching or engraving the steel caul plates with the desired pattern is quite expensive, with the result that the cost of producing fiberboards having textured surface finishes by this method is excessively high. A large number of die plates are needed even if only a moderate selection of patterns are to be provided by the manufacturer. The plates are easily damaged and must be frequently replaced.

The present invention overcomes these disadvantages by providing a low cost disposable sheet with a threedimensional pattern of substantially non-crushable material. The sheet is interposed between a plain smoothsurfaced caul plate or press platen and the fiber mat during the pressing operation. The patterned impression sheet eliminates the need for the much more expensive patterned steel caul plate. While the impression sheet is sufiiciently low in cost to permit disposal after a single use, the sheet may be used for additional pressings if undamaged after its initial use.

The impression sheet is also useful in embossing the surface of decorative laminates during hot-pressing operations, as hereinafter described.

SUMMARY OF THE INVENTION In one preferred form of the invention, a sized paper sheet is first coated on one side with a release coating, such as a talc-clay mixture. This sheet is then embossed with a desired patern, for example, a simulated Wood grain. The embossed portions of the sheet are then backfilled with a substantially non-compressible filler coating, such as a clay-thermosetting phenolic resin mixture. After being applied, the coating is cured to set the resin. The patterned sheet is then ready for use as a disposable impression sheet, and is interposed between the upper caul plate or platen of a hot press and the fibrous mat which has been inserted in the press, for consolidation into hardboard. Since the patterned coating on the impression sheet is relatively uncompressible under the pressures involved, it will impress the pattern into the fiberboard surface during the pressing operation. The

depth of the embossed pattern may be varied depending upon how much contrast is desired in the patterned fiberboard. Generally, this depth is greater than the thickness of the sheet to provide a readily visible pattern.

One method of using the above-described impression sheet for making textured hardboard is first forming a wet lap of coarse fibrous pulp of about 40' percent consistency, then applying to the surface of the formed fibrous mat a finished sheet of paper previously printed with a selected decorative pattern, overlaying the printed paper sheet with the impression sheet of this invention which has a pattern compatible with the selected printed pattern and pressing the lay-up to consolidate the wet lap and decorative paper by heat and pressure, whereby the decorative paper and fibrous mat are bonded together into a unitary fiberboard, and the pattern from the impression sheet is impressed intol the fiberboard surface. After removal from the press, the impression sheet is stripped from the finished board, or it may be left on temporarily to protect the surface during subsequent handling. The impression sheet may be discarded after this one use, or if undamaged, may be used for additional pressings. The raised pattern of the impression sheet is embossed into the surface of the fiberboard. If a wood pattern has been selected, the fiberboard would then have the appearance and feel of grained wood'. It willbe seen that this ,invern-V tion is therefore capable of providing an infinite number of patterns at low cost.

In another equally satisfactory embodiment of the invention, the sized paper sheet, instead of being embossed and backiilled, is printed with a raised, three-dimensional pattern of the same non-compressible mixture described above. A patterned intaglio roll, suitable stencil, or engraved roll, of types known in the printing trade, may be used to apply the material to the sized paper in the form of a raised pattern in the desired configuration. As before, a release coating is also applied to the underside of this sheet. When the impression sheet produced in this manner is inserted into the forming press as a substantially non-crushable embossing element, the pattern provided by the sheet will be reproduced on the surface of the fiberboard.

The impression sheets described herein are also useful in embossing the surface of decorative laminates during conventional hot-pressing operations.

It is therefore an object of the present invention to provide a liexible sheet having a three-dimensional stable pattern applied thereto for use as an impression sheet for impressing a selected textured pattern into the surface of iberboard panels, decorative laminates, or the like.

Another object is to provide a low cost disposable irnpression means for use in manufacturing decorative fiberboard panels having a three-dimension embossed surface.

Still another object is to provide a method for making a disposable impression sheet for use in fabricating textured iiberboard,

Other objects and advantages of the invention will be understood by reference to the following specification and accompanying drawing wherein there is described and illustrated selected forms of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of a coating, embossing, and backfilling method for preparing the impression sheet.

FIG. 2 is a diagrammatic illustration of a method for printing the impression sheet with a raised pattern.

FIG. 3 is an exploded view of a preferred arrangement of the impression sheet, a paper decorative layer, and fibrous mat as arranged in a press prior to consolidation of a wet mat into a finished board.

FIG. 4 is similar to FIG. 3 but shows the arrangement of the sheets in a press when the dry pressing process is used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a roll 11 of sized paper is fed through a coating nip 6 comprising a smooth-faced coating roll 7 and a back-up roll 10, for the application of a release coat to the paper. A preferred release coating material is an aqueous dispersion of a clay-talc mixture 9 disposed in dip pan 8. Application roll 7 applies a surplus amount of coating to the paper which is then smoothed and doctored olf by doctor blade 5. The coated sheet then passes through a drier section 27 which may comprise air or radiant heating elements 28 and 29. The dried paper then proceeds around idling roll 4 to embossing nip 13 comprising an embossing roll 12 having a selected pattern engraved on its surface and a backup roll 14 of resilient material. After embossing, the embossed sheet 15 is coated and backlled by passing it over a coating roll 17 which rotates in dip pan 18, containing a clay-phenol-formaldehyde mixture 19. Roll 17 picks up the coating mixture 19 and applies it to embossed sheet 15, without destroying the embossments, and in a suicient quantity to lill the cavities in the sheet provided by the embossing operation. Roll 17 may be rotated at various speeds in either direction as indicated by arrow 16 depending on the amount of coating desired. Floating doctor blade 21 removes any excess coating from the sheet and the excess material is returned to dip pan 18. The filled sheet then passes around 4 rolls 20 and 22 through a drying and curing section 23 which may comprise heating means 24 and 25 to cure and set the resin binder in the backfill coating. The coated, embossed, backlled, and cured sheet is then wound up on roll 26.

In FIG. 2 a roll 31 of sized paper is fed through a coating nip 43 comprising a smooth-faced coating roll 48 and a back-up roll 44 for the application of a release coating to one surface. The preferred release coating is an aqueous dispersion of talc and clay disposed in dip pan 46. Applicator roll 48 transfers a surplus amount of coating to the paper surface whereafter it is smoothed and the surplus removed by doctor blade 47. The coated web then passes through drying section 49 which may comprise heated elements 50 and 50a of known types. After the release coating is dried the web passes around an idling roll into printing couple 33 comprising an intaglio printing roll 32 and back-up roll 34. Printing roll 32 picks up a supply of coating material 35 from pan 36. The excess coating is doctored off printing roll 32 by doctor 37 and roll 32 then applies a raised pattern 38 of coating to the paper. The paper with the raised pattern coated on one side then passes through a drying and curing section 39 which may comprise heating means 40` and 41 to cure and set the raised pattern. The treated sheet is then Wound up on roll 42.

Either the embossed `and backfilled sheet, or the sheet printed with a raised pattern, is now ready for use in texturizing the surface of the iiberboard.

A known means for the pressing operation is shown in FIG, 3. A thick fibrous mat of coarse fibers 51, carried on wire screen 56 in moist condition, makes up the bottorn lamina and comprises the main board structure. Over this mat is placed a decorative sheet 52 of line bered paper preferably printed in a selected color or pattern, and over this is placed the impression sheet 53, prepared as previously described and the patterned side up and release coated side down. Upper and lower platen press sections 54 and 55 of the hot press are then pressed together to drive off the remaining moisture, consolidate paper sheet 52 with fiber mat 51, and impress the pattern of impression sheet 53 into the surface of the hardboard. After the press is released, impression sheet 53 is stripped olf.

As indicated above, the base paper for the impression sheet is a sized paper. While acid-sized paper may be used, it was found that conventional rosin-sized paper had a tendency to char in the hot press operation. Any paper used should be substantially heat stable so that it does not deteriorate to any large degree under the heat used in the pressing operation. Accordingly, alkalinesized paper is preferred. One such type of sizing is known as Aquapel, a series of alkylketene dimers prepared from long chain fatty acids. While various basis weights may be used, basis weights ranging from 12 lbs. to 20 lbs. per ream 17 x 22-500 sheet rearns are presently preferred. As indicated, it is apparent that basis Weights outside the preferred range may also be used.

A thin metal foil may be substituted for the sized paper as the base material. However, such foils are relatively more expensive and would require more care in handling because of their tendency to wrinkle permanently.

The coating material used in applying the three-dimensional pattern to the sized paper should comprise a substantially non-compressible material. The material in its cured form, should have suiiicient strength so that it does not shatter or crush during the hot press operation. Mixtures of kaolin clay and thermosetting resins have proved satisfactory; as have mixtures of clay, microscopic glass beads, and thermosetting resins. Some organic fillers such as wood flour have also proved satisfactory. Other line mineral liller may be used as long as they do not crush under the pressures involved, or decompose under the high temperatures used, in the board pressing operation. Phenol formaldehyde is the preferred resin but other thermosetting resins such as urea formaldehyde, melamine formaldehyde, epoxies, and the like may be used.

In one specific example of a preferred embodiment for the coating is a formulation consisting of 20% phenol formaldehyde resin, 16% kaolin clay and 64% microscopic-sized glass beads dispersed in water at about 70% solids. Various ratios of the above mixture may be used. Useful ranges comprise about 15 to 35% resin; 16% to 85% kaolin clay; and 0% to 60% glass beads. The glass bead size preferred is in the range of l to 53 microns, but larger sizes may be used.

The preferred release coating comprises about 4 parts bentonite clay, 1'8 parts talc and 7S parts water. Mixtures in the range of 0 to 8 parts clay; 6 to 36 parts talc', and 54 to 90 parts water may be used. In the embodiment, described herein, the release coat might better be characterized as a low cohesive strength parting coat. A description of its mechanism and how it functions appears in order. A talc coating laid from an aqueous dispersion has very little strength. The bentonite clay is used in combination with the talc at relatively low levels as a means of controlling viscosity and keeping the talc in suspension. It is believed that the bentonite clay at the level used does not necessarily act as a binder to increase the strength of the dried talc coating. In use, it has been found that the talc coating splits when the paper impression sheet of this invention is removed from the pressed board and part of it remains on the board surface. The small amount of talc remaining on the board is completely innocuous to subsequent coating materials used for finishing the board. When the board is linished with pigmented paints, the talc simply becomes a small additional part of the extender or filler system used in the paint, since talc itself is frequently used as an extender in paints. In the case of finishing with a clear top coating, the talc is present at such a low level and has an index of refraction so near that of the paint binder that its presence is undetected.

The virtues of talc then are: (l) it has the right level of adhesion to the paper impression sheet to remain intact during processing and handling; (2) it has the right level of cohesive strength to remain intact during processing and handling and yet to provide a parting layer when removed from the pressed board without delaminating the paper impression sheet; (3) it is innocuous to subsequent linish coatings; (4) it is very cheap; (5) it has high heat stability, i.e., does not melt or decompose; (6) it handles well in the method of application described.

Other low cohesive strength parting coats utilizing this principle, or an ordinary release coating may be used. For example, as another low cohesive strength parting coat one might use clay with a low level of starch binder. For other release materials one might use silicones, fluorocarbons, tetrauoroethylene resins, and the like, in instances when their expense is justified. The latter type release materials are especially useful when the impression sheet is to be used for embossing decorative laminates.

There are presently in commercial use, two well known pressing operations for hardboard in which the impression sheet may be used. In the wet process, a fiber mat is formed on a fourdrinier wire and pressed to 40% consistency. A plain or printed overlay sheet of paper is run on top of the wet mat and the impression sheet of this invention is fed on top of the overlay. The three sheets are simultaneously cut to length and fed to a hot press, into which they are carried on a wire screen. After the sheets are inserted, the press is closed and the sheet subjected to pressures varying from 50 to about 770 p.s.i. at temperatures of about 390 F. during a pressing cycle of about 8 to 9 minutes after which time the press is opened and the panels discharged. The impression sheet is then stripped from the finished panel leaving a mirror image of the pattern on the Iiberboard surface. The pressed board may also be passed to a baking oven for further treatments if drying oils are used in its construction. FIG. 3 illustrates the arrangement of the sheets in a suitable platen press for the above-described operation.

In the dry process, the fiber mat is formed on a wire, then oven-dried and supplied to the press at a density of about 20 lbs. per cubic foot. No overlay sheet is used. The patterned impression sheet of this invention is placed on ktop of the dry vmat as it goes into the press. Depending on kthe iinished thicknesses and densities desired the mat is pressed for about seconds at temperatures up to 470 F. and pressures in the range of 500 to 1000 p.s.i. After pressing the board is allowed to cool and the impression sheet stripped off leaving a permanent pattern on the board surface.

FIG. 4 illustrates the arrangement of sheets for the dry pressing process. The dry mat is 61, the patterned impression sheet is 62 and the upper and lower press platens are 63 and 64 respectively.

After patterning, the board has the patterned surface finished by applying an opaque coating suitable to the type of pattern applied. For example, if the pattern is simulated leather, a finish having a leather-like tone is applied. If the pattern is a tile pattern, a hard, shiny enamel-like finish is applied.

The impression sheets of this invention may also be used to impress embossments simultaneously on both sides of a berboard sheet.

The impression sheets are also useful as the embossing means for decorative laminates of both the high pressure and low pressure types.

However, when used as the embossing means during the hot pressing process employed in the manufacture of such decorative laminates, the base paper for the impression sheet preferably should be of a type which is impervious to the hot flow of uncured resin which takes place during the laminating process. Base sheets having this property include glassine paper, vegetable parchment paper, or the previously mentioned aluminum foil. Also, when used in embossing decorative laminates, it is preferred that the release coat employed be a non-transferring release agent such as the previously mentioned silicones, fluorocarbons, tetrafluoroethylene resin or the like. If the low cohesive strength parting coat were employed, it would transfer a portion of the coating to the embossed surface, which is undesirable when a high gloss surface finish is intended on the decorative laminate.

The construction of conventional decorative laminates is well known in the art. It generally comprises a base or core member which functions to impart rigidity to the laminate, a print sheet member, and a protective overlay.

The core member usually comprises a plurality of sheets of kraft paper impregnated with a phenolic resin, although other materials may be used. The core member may be cured before or during the final laminating and embossing operation.

The print sheet member generally comprises a single sheet of a good grade of absorbent alpha cellulose or regenerated cellulose paper impregnated with an aminotriazine-aldehyde resin, usually ymelamine-formaldehyde. Polyester resins are also sometimes used.

Finally, the protective overlay generally comprises a single sheet of high grade alpha cellulose paper impregnated with an aminotriazine-aldehyde resin similar to or the same as that used in the print sheet member. If a polyester resin is used in the print sheet member, a similar polyester should also be used in the overlay.

The process of laminating, pressing and heat curing these sheets to produce conventional decorative laminates is also well known. The following general description will illustrate how the impression sheet of this invention is used in the process when surfaceembossing is desired.

The impression sheet is prepared as previously described except that the base sheet used in glassine paper, or vegetable parchment paper, or other similar relatively impervious material. Also, the sheet is coated with a nontransferable release coat on the side opposite from the patterned coating.

A laminating assembly includes, as bottom layers, multiple sheets of phenolic-impregnated kraft; as an intermediate layer, a decorative print sheet impregnated with melamine resin; and as the top layer a protective sheet of translucent alpha-cellulose impregnated with a melamine resin. The above-described impression sheet with the release coat facing down is then positioned on the top sheet and the entire assembly inserted between a pair of stainless steel or similar press plates and consolidated in a laminating press at a temperature about in the range of 275 F. to about 340o F. and pressures ranging from about 600 to about 1500 p.s.i. The time required to effect substantially complete cure of the resinous components when employing temperatures and pressures within the above stated ranges varies with the resin employed but will usually be from about 6 minutes to about 45 minutes. While the laminate may be removed while hot, it is generally allowed to cool to a temperature of less than about 110 F., and preferably to room temperature before being removed from the press. After removal and cooling, the impression sheet is stripped off and a mirror image of the selected pattern remains.

FIG. 4 is also illustrative of the manner in which the modified impression sheet may be used for the hot-pressing of decorative laminates. ln this case, 62 represents the modified impression sheet while 61 represents the laminated assembly before pressing.

The degree of gloss in the surface iinish of the laminate may also be controlled to some extent by the smoothness of the base sheet employed for the disposable impression sheet. Highly calendered glassine, for example, will give a highly polished linish. A matte finish may be obtained by using a matte finish base sheet.

Decorative laminates may also be embossed with an impression sheet, as earlier described, in which the base paper is not impervious to the flow of heat-activated resin. However, in such an event, it is necessary to interpose an impervious sheet between the impression sheet and the assembly being laminated. The impervious sheet thus would prevent resin migration in the same manner as when the impression sheet itself comprises an impervious material. The use of a separate impervious element may be less desirable than the embodiment in which the impervious is an integral part of the impression sheet itself, since the former requires handling a separate element during the laminating and curing operation.

The sheet may also be used in embossing low pressure decorative laminates in which a laminating assembly of resin-impregnated decorative sheets are used in combination with a low density substrate such as iir plywood, hardwood plywood veneers, particle boards and hardboards. In such instances, the same times and temperatures as previously described for high pressure laminates are used but the pressures used are in the range of 250 to 350 p.s.i.

What is claimed is:

1. A disposable impression sheet for use in embossing predetermined patterns into the surface of deformable panel stock, said sheet comprising a iiexible heat stable web, embossments projecting outward from the normal plane of said web in a predetermined pattern, and cavities behind said embossments on one side of Said sheet filled to the level of said normal plane with a substantially non-compressible material; said non-compressible material being stable when subjected to heat and pressure, and comprising a mixture of non-crushable liller and a cured thermosetting resin.

2. The sheet of claim 1 in which the side of said sheet opposite from said filled side is coated with a continuous release coating.

3. The sheet of claim 2 in which said release coating is of low cohesive strength and comprises a mixture of bentonite clay and talc.

4. The sheet of claim 1 in which said non-compressible material comprises a mixture of kaolin clay and a cured thermosetting resin.

S. The sheet of claim 4 in which the thermosetting resin is selected from the group consisting of phenol formaldehyde, urea formaldehyde, melamine formaldehyde, and epoxies.

6. The sheet of claim 1 in which said non-compressible material comprises a mixture of kaolin clay, microscopic sized glass beads, and a cured thermosetting resin.

7. The sheet of claim 6 in which said non-compressible material comprises from 16% to 85% kaolin clay, 0% to 60% glass beads, and 15 to 35% of a cured thermosetting resin.

8. The sheet of claim 1 in which the iiexible heat stable web comprises alkaline-sized paper.

9. The sheet of claim 8 in which said alkaline size is an alkylketene dimer prepared from long chain fatty acids.

10. The sheet of claim 1 in which said flexible web is a thin metal foil.

11. A disposable impression sheet for use in embossing predetermined patterns onto the surface of decorative laminates during hot-press lamination, said sheet cornprising a iiexible heat stable web which is impervious to the iiow therethrough of heat activated thermosetting resin, embossments projecting outward from the normal plane of said web in a predetermined pattern, and cavities behind said embossments on one side of said sheet lled to the level of said normal plane with a substantially non-compressible material; said non-compressi-ble material being stable when subjected to heat and pressure, and comprising a mixture of non-crushable ller and a cured thermosetting resin.

12. The sheet of claim 11 in which the side of said sheet opposite from said iilled side is coated with a 40 continuous release coating.

13. The sheet of claim 11 in which said non-compressible material comprises a mixture of kaolin clay and a cured thermosetting resin.

14. The sheet of claim 13 in which the thermosetting resin is selected from the group consisting of phenol formaldehyde, urea formaldehyde, melamine formaldehyde and epoxies.

1S. The sheet of claim 11 in which said non-compressible material comprises a mixture of kaolin clay, micro- 50 scopic sized glass beads, and a cured thermosetting resin.

16. The sheet of claim 11 in which said impervious web is selected from the group comprising glassine paper, vegetable parchment paper and thin metal foil.

17. The sheet of claim 12 in which said release coating is selected from the group consisting of silicones, fluorocarbons, and tetratiuoroethylene resins.

References Cited UNITED STATES PATENTS U.S. Cl. X.R. 

